feat(#536): add support .csv files for open_fixture

[HairlessVillager]

Description

Add comprehensive CSV file support to the open_fixture and open_fixture_async functions, expanding the fixture loading capabilities beyond JSON to include comma-separated value files.

Closes

Closes #536

[codecov-commenter]

Codecov Report

❌ Patch coverage is 65.78947% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.29%. Comparing base (82a8cee) to head (fe8e323).

Files with missing lines	Patch %	Lines
advanced_alchemy/utils/fixtures.py	65.78%	24 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #615      +/-   ##
==========================================
- Coverage   80.35%   80.29%   -0.06%     
==========================================
  Files          87       87              
  Lines        6433     6486      +53     
  Branches      838      846       +8     
==========================================
+ Hits         5169     5208      +39     
- Misses       1000     1014      +14     
  Partials      264      264              

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[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/advanced-alchemy-docs-preview/615